Disk Preparation Tool With Flexible Cutting Element

ABSTRACT

A tool for preparing vertebral surfaces following a discectomy has a body and a rotary cutting tool mounted at the distal end of a lever which extends through the body. The proximal end of the lever can be squeezed toward the body to force the cutting tool against the vertebral surface facing it, while the tool is rotated by turning a crank supported on the tool body, or by a motor. The cutting tool is preferably a flexible rasp or blade which can conform to and control the convexity of the prepared surface.

This application is a continuation of copending application Ser. No.11/692,878 filed Mar. 28, 2007, which claimed benefit of provisionalpatent application 60/786,394, filed Mar. 28, 2006.

BACKGROUND OF THE INVENTION

This invention relates to an intervertebral disc removing device. Itallows for removal of the nucleus pulpous of an intervertebral disc, aswell as the resurfacing of the vertebral end plate in preparation fornucleus replacement procedures or interbody fusion techniques.

Of all animals possessing a backbone, human beings are the onlycreatures who remain upright for significant periods of time. From anevolutionary standpoint, this erect posture has conferred a number ofstrategic benefits, not the least of which is freeing the upper limbsfor purposes other than locomotion. From an anthropologic standpoint, itis also evident that this unique evolutionary adaptation is a relativelyrecent change, and as such has not benefitted from natural selection asmuch as have backbones held in the horizontal attitude. As a result, thestresses acting upon the human backbone (or “vertebral column”) areunique in many senses, and result in a variety of problems or diseasestates that are peculiar to the human species.

The human vertebral column is essentially a tower of bones held uprightby fibrous bands called ligaments and contractile elements calledmuscles. There are seven bones in the neck or cervical region, twelve inthe chest or thoracic region, and five in the low back or lumbar region.There are also five bones in the pelvic or sacral region which arenormally fused together and form the back part of the pelvis. Thiscolumn of bones is critical for protecting the delicate spinal cord andnerves, and for providing structural support for the entire body.

Between the vertebral bones themselves exist soft tissuestructures-discs-composed of fibrous tissue and cartilage which arecompressible and act as shock absorbers for sudden downward forces onthe upright column. More importantly, the discs allow the bones to moveindependently of each other, as well. Unfortunately, the repetitiveforces which act on these intervertebral discs during repetitiveday-to-day activities of bending, lifting and twisting cause them tobreakdown or degenerate over time.

Presumably because of humans' upright posture, their intervertebraldiscs have a high propensity to degenerate. Overt trauma, or coverttrauma occurring in the course of repetitive activities,disproportionately affect the more highly mobile areas of the spine.

Disruption of a disc's internal architecture leads to bulging,herniation or protrusion of pieces of the disc nucleus and eventual discspace collapse. Resulting mechanical and even chemical irritation ofsurrounding neural elements (spinal cord and nerves) cause pain,attended by varying degrees of disability. In addition, loss of discspace height relaxes tension on the longitudinal spine ligaments,thereby contributing to various types of spinal instability such asspinal curvature, ligamentous laxity or instability andspondylolithesis.

The time-honored method of addressing neural irritation and instabilityresulting from severe disc damage have largely focused on removal of thedamaged disc and fusing the adjacent vertebral elements together.Removal of the disc relieves the mechanical and chemical irritation ofneural elements, while osseous union (bone knitting) solves the problemof instability.

Once the disc has been removed, an implant may be installed in itsplace. Prior to implantation, in many situations, it is desirable ornecessary to smooth or recontour the opposing vertebral surfaces. Properpreparation can be difficult and time-consuming.

U.S. Pat. No. 6,537,279 depicts a device for preparing an intervertebralendplate with an abrading element which is disc shaped.

In contrast, the abrading element of my device is linear and rotatedlike a propeller so it can be inserted through a much smaller opening ina disc and lends itself to minimally invasive techniques. Prior deviceshaving disc-shaped cutters required an opening to be made in the discannulus comparable in size to the diameter of the disc. The slendercutter of the present invention can be inserted through an opening muchsmaller than that required by a disc shaped cutter and hence is superiorfor minimally invasive techniques.

The present device also does not require screws to hold it in place inthe disc space; moreover, the cutting surface can be expanded within thedisc space to achieve greater force against the end plates. In contrast,the distance between the disc shaped cutters in the patent mentionedabove is fixed by the gear drive mechanism used to drive both cuttingdiscs simultaneously.

Because the abrading surfaces can be pressed apart while within the discspace, varying disc heights can be accommodated with a single device.

The device of the present invention has a flexible cutting blade whichconforms itself to various contours in the endplate whereas priorcutting surfaces are fixed and their contours are predetermined, notvariable. The propeller-like shape of the cutting or abrading surface issuperior because it can be inserted through an opening the width of thepropeller blade and still resurface a disc sized the length of thepropeller blade.

One embodiment of the present invention has a dual shaft design whichallows the abrading surfaces to be expanded away from each other toallow for use in discs of any height without any change of the drivemeans or the abrading elements. Additionally, the dual shaft design issuperior as it allows the working cutting blades to be driven apart fromeach other to increase the force upon the blades while the blades arestill in motion.

SUMMARY OF THE INVENTION

An object of the invention is to improve the speed and quality ofvertebral surface preparation following a discectomy.

Another object is to provide a tool that can be inserted into anannulotomy in an intervertebral disc to simultaneously or sequentiallyperform the functions of disc removal, end plate preparation, irrigationand suctioning without having to be removed.

A further object is to provide a tool for disc removal and end plateresurfacing which can be inserted into a disc space, centered (by meansof x-ray localization) and fixated in position by a pin located at therotary head, the pin serving to engage a vertebral surface and steadythe tool.

These and other objects of the invention are attained by the surgicaltool described and claimed below.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings,

FIG. 1 is a top plan view of a tool embodying the invention,

FIG. 2 is a left side view thereof,

FIG. 3 is a bottom plan view thereof,

FIG. 4 is an enlargement of a portion of FIG. 2, showing the cuttinghead of the tool,

FIG. 5 is a similar view, showing flexure of a rasp mounted on the head,

FIG. 6 illustrates placement of the tool head within a surgical site,

FIG. 7 shows the tool being used to prepare a vertebral surface,

FIG. 8 shows a tool in which the cutting head is driven by a smallmotor, and

FIG. 9 shows an alternative form of the invention, having two opposedcutting heads.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE INVENTION

A tool embodying the invention has a pistol-shaped body 10 whose lowerportion is shaped to form a hollow grip 12 preferably having fingerdepressions 14 as shown in FIG. 1. The forward or distal end of the bodyis an elongate probe 16 that tapers towards its tip 18. A fixedcentering pin 20 extends downward from the tip.

The body contains a portion of a lever 22, which is supported on atransverse pivot pin 24 seated in holes (not shown) in the body.Alternatively, the pin might be molded integrally with the body andholes formed in the lever, or pin ends could be molded on the lever, forseating in the holes in the body.

The proximal end of the lever 22 extends downwardly, to the rear of thepivot pin. Its rear surface 26 is rounded to fit against the palm of asurgeon. A reduced-thickness guide portion 28 formed to the front of therear surface is sized to slide in and out of the cavity in the grip, tomaintain alignment between the parts.

A lock actuating lever 30 at the bottom of the grip can be moved betweena safe position preventing movement of the lever and an operatingposition permitting movement.

The distal end 32 of the lever is a slender tube substantially parallelto the probe 16, and having a distal terminus 34 near the tip 18.Alignment between the probe and the tube is maintained by an alignmentstem 36 which extends from the shaft into a hole or slot in the probe. Aright angle drive mechanism 38 is fixed at the terminus 34. Themechanism has an output shaft (not shown) that rotates about a head axis“A”. A rotary head 40 is secured to the output shaft, and a flexiblerasp 42 or blade is mounted on the rotary head. The blade or rasp isdesigned to cut material from an intervertebral disc end plate and todirect cuttings downward to a suction port for removal. It can be raisedor lowered mechanically by the lever mechanism to enhance its efficiencyand effectiveness. Its flexibility enables it to conform toirregularities in the shape of intervertebral disc or the adjacent endplate, so that it does not have to grind a geometric surface ofrevolution on the end plate.

Preferably, the shape of the blade is propeller-like, and its length issubstantially greater than its width. The aspect ratio (length-to-width)of the blade is preferably at least 3:1, and may be substantiallygreater than that. The narrower the blade is, the smaller a surgicalaperture it may be inserted through.

The thickness and material of the blade are chosen so that the blade,without being flaccid, can deflect from its original shape to followirregularities it encounters in the end plate without undergoing anypermanent deformation so that it always returns to its original shapewhen load is released. It should be sufficiently stiff (resistant tobending) that its outer edges remain in contact with the end plate inuse, yet not so stiff that it cuts more at the tips of the blade than atthe center, or so stiff that it is difficult for the surgeon to applyenough squeezing force to the handle to establish full contact betweenthe blade and the endplate. Ideally, the blade should apply evenlydistributed pressure to the end plate. An assortment of blades ofdifferent sizes, shapes, stiffnesses and surface may be provided for thesurgeon to choose from.

The rasp head is turned, an will be explained, by a crank mechanismshown generally as 44, at the proximal end of the tool. The mechanismcomprises a crank arm 46 having a handle 48, and a crank shaft, notshown, inside the tool. A transmission device, such as a beveled gearset or a flexible drive cable, connects the crank shaft to a drive shaft(not shown) inside the tube. The drive shaft serves as, or is connectedto, the input shaft of the right angle drive so that, when the crank isturned, the rotary head and the rasp mounted thereon turn as well.

A water supply line 50 and a suction line 52 extend along parallel pathsthrough the body of the tool, terminating at neighboring outlet ports54, 56 directed at the bottom of the rasp.

In use, a surgeon, having made a suitable incision and having performeda discectomy, inserts the tip of the tool through the incision into thespace previously occupied by the disc. The surgeon carefully centers thetip of the tool in the intervertebral cavity, as shown in FIG. 6, andpresses the centering pin into the surface of the vertebra opposite thatbeing prepared to steady the tip as the tool is operated. Now the raspmay be caused to bear against the subject surface by applying controlledpressure to the palm actuator (FIG. 7). Because the rasp is flexible,the more pressure is applied (compare FIGS. 4 and 5), the more the raspwill bend as it engages the convex surface. By controlling the pressure,the degree of convexity in the subject surface can be controlled aswell.

The rasp is rotated by turning the crank handle, and as it rotates, therasp removes material from the subject surface. The cuttings, flushedaway from the rasp by incoming water from the supply line, are removedfrom the site by the suction line.

This invention is subject to modification and improvement, and numerouschanges may occur to a person of ordinary skill in this field. Detailsof the drive train between the crank shaft and the right angle drive arematters of ordinary skill.

Alternatively, the crank may be replaced by a motor, such as a hydraulicmotor driven by the supply water; that motor could be placed in the bodyof the tool, or possibly in the position of the right angle drive, asshown in FIG. 8—where the motor is designated by reference numeral 60—inwhich case no drive train would be needed. The motor might be electric,hydraulic or pneumatic. Also, the materials, sizes and proportions ofthe elements of the invention may be altered for various purposes andsituations.

As a further modification, a second rotary head may be positioned at thetip of the tool, the heads being substantially aligned on a common axisand facing in opposite directions so that opposite end plates may beprepared simultaneously. This modification is shown in FIG. 9, thesecond head being identified by reference 40′. The heads areindependently driven, for example by respective drive shafts, or byindependent motors at the tip of the probe 16 and the distal end of thelever 32. An advantage of providing independent drives is that thesurgeon can vary the distance between the cutters while both are inoperation. If the cutters are turned in opposite directions, reactiontorques on the tool are canceled.

Considering the numerous modifications that are possible, the embodimentillustrated should be understood as only exemplary, and the inventionshould be measured by the claims below.

I claim:
 1. A tool for preparing a surface of a vertebral body, saidtool comprising: a body, a rotary head supported on the body, amechanism for turning the rotary head, and a cutting tool mounted on therotary head.
 2. The invention of claim 1, wherein the cutting tool is aflexible rasp.
 3. The invention of claim 2, wherein the aspect ratio ofthe blade is preferably at least 3:1, so that it may be inserted througha small surgical aperture.
 4. The invention of claim 2, wherein thethickness and material of the blade are chosen so that the blade,without being flaccid, can deflect from its original shape to followirregularities it encounters in the end plate without undergoingpermanent deformation.
 5. The invention of claim 1, wherein the cuttingtool is a flexible blade.
 6. The invention of claim 5, wherein theaspect ratio of the blade is preferably at least 3:1, so that it may beinserted through a small surgical aperture.
 7. The invention of claim 5,wherein the thickness and material of the blade are chosen so that theblade, without being flaccid, can deflect from its original shape tofollow irregularities it encounters in the end plate without undergoingpermanent deformation.
 8. The invention of claim 2, wherein the cuttingtool rotates around its longitudinal axis while simultaneously turningwith the rotary head.
 9. The invention of claim 1, further comprising atleast one water supply line extending through the body to a portdirected at the rotary head, to flush cuttings away, and at least onesuction line extending through the body to at least one port in thevicinity of the rotary head, to remove cuttings from said vicinity.